TITLE:   GCN CIRCULAR
NUMBER:  18362
SUBJECT: LIGO/Virgo G184098: ongoing Pan-STARRS search for optical transients
DATE:    15/09/24 13:29:47 GMT
FROM:    S. J. Smartt at Queens U Belfast  <s.smartt@qub.ac.uk>

S.J. Smartt, K. W. Smith,  (Queen��<80><99>s University Belfast), K. Chambers,
M. Huber, E. Magnier, H. Flewelling, C. Waters, J. Tonry, A. Schultz,
N. Primak (IfA, University of Hawaii), D. Young, D. Wright
(Queen��<80><99>s University Belfast), C. Stubbs (Harvard)

Following our reports of Pan-STARRS pointing coordinates for the field
of LIGO/Virgo G184098 and the search for transients, an update is provided
here. The coordinates of 4 nights of observations are given on the GraceDB
webpages. Images in i, z and y-band were taken on 2015-09-17, 19, 22, 23.
The difference images were processed as described in Huber et al.
(Atel 7153) and on the Pan-STARRS Survey for Transients (PSST) pages
(http://star.pst.qub.ac.uk/ps1threepi/psdb/).

We initially reported first night detections of PS15cbm, PS15cbj, PS15cbn
(2015-09-17). However subsequent data show that only PS15cbm is real.
The other two were not recovered in later images and are almost certainly
instrumental ghosts.

Over these four nights, we now have 5 objects which are detected in multiple
nights and multiple filters (and different camera orientations) and are likely to be
extragalactic transients  (they are all associated with a galaxy in SDSS and PS1
reference images).

Obj      RA(J2000)    Dec(J2000)   mag      z
PS15cbm  08:49:19.85  +03:48:17.8  18.54(i) 0.059
PS15cci   09:13:22.76  +06:10:47.2  18.33(i) ��<80>��
PS15ccx  08:18:03.90  +04:18:04.2  19.42(z) ��<80>��
PS15ccv  08:55:23.07  +04:41:19.0  19.57(i) 0.071
PS15ccw  08:57:30.60  +04:31:56.1  19.33(i) 0.072

The mag is the discovery magnitude (AB system). The reported
redshift is the spectroscopic redshift of the apparent host galaxy from SDSS DR12.
The other two have no spectroscopic redshifts, but have detected host galaxies.
>From the data in hand, all appear to be likely supernovae. 

The object furthest north-east (PS15cci) is close to the 90% confidence contour
of the G182098  'LIB_skymap' GW localisation map. The others are
outside this region but within the 'skyprobcc_cWB��<80><99> map. Twilight restricted us
pointing at the centre of the 'LIB_skymap' GW localisation map. Our survey area is
slightly further south than the iPTF survey area (Singer et al. GCN 18337) and the
J-GEM area (Morokuma et al. GCN 18361). Observations are continuing this week
when the weather cooperates.